My wife went to let the dog out this morning and came running back in shouting that my bike was leaking all over the place.

Sure enough, there was a miniature BMW themed waterfall of fuel dumping onto the ground. Seemed to be originating from the rear of the tank, near the fuel sender, but I couldn't entirely tell. When I lifted up the rear of the tank to get a better look there was a hissing sound of air escaping from somewhere, so I got my key and opened the fill cap. There was a very loud hissing from the cap and a bunch of air vented, and shortly thereafter the leaking slowed to a tiny trickle and then stopped.

I'd just put about 3 gallons into the tank yesterday, and where it was parked it was in the sun for a few hours this morning. I assume the heat built up pressure in the tank and it vented out of somewhere it shouldn't have, but where? And why the heck doesn't the tank have a proper vent to keep this from happening?

How do I take the tank off and fix it without loosing all my fuel?

Help?

I don't think you'll loose fuel by taking the tank off the bike, I've taken mine off a few time, got a few drips but that was it. No fuel leaked out after I had taken the fuel pipes off. I may be wrong as only going by my own experiance.

Due regulations about environment bla..bla.. US models have tank vent system leading the fumes down to the crankcase via a hose with a valve, and then later be sucked into the engine and burned.

I`ll guess your valve doesn`t function properly.

Not unusual that bikes "over there" rebuild the tank ventilation to the euro version.

Thanks for the information, is there any way I can go about testing the tank vent to see if it functions? A cursory inspection shows a few different hoses coming out of the bottom of the tank, most of which stick out about an inch before terminating in a mangled, dry rotted mess...

At the rear right under the tank you got two spigots, the most forward one is for the ventilation, and should be open into the tank.

This is valid on a -86. and later.

Since no info provided what you got..........................

Thanks, forgot to say it's a '92 K100 RS. California model, so I'm sure it's got every emissions control system under the sun...

How do I get the tank off?

Thank you! Looks relatively simple. So basically I should inspect and replace both breather hoses and ensure the fuel sender gasket isn't compromised?

According to the link as long as both hoses drain to the ground everything is safe and correct, yes?

I think your overpressure and fuel leak is ~~two different issues.........that the gasket allready must have been very weak.

If you got enough pressure in the tank to blow the gasket, in my opinion the vent hose should burst way before that as these hose isn`t reinforced...........unless its earlier have been changed.

Also have a look at this: http://www.motobrick.com/index.php/topic,989.0.html

Got it, so to be on the safe side I should go ahead and replace the sender gasket ring?

I'm wondering since it stopped when I vented the pressure if it's not completely broken. I guess we'll find out when I get the tank off.

Kingsly wrote:Got it, so to be on the safe side I should go ahead and replace the sender gasket ring?

Better safe than sorry......when the alternative is roasted nuts along the highway.

Agreed.

Kingsly wrote:According to the link as long as both hoses drain to the ground everything is safe and correct, yes?

Hi there, the link is not mentioning that the hose connected to the on the top front of the engine block has a calibrated check valve to control the flow and avoid the return. This assemble was modified by BMW due to possible engine damage caused by oil contamination by fuel flowing in excess under high temperatures. Modiffication consist on re routing the hose paralell to the other one and shutting the connection point on the engine. In my bike the other hose serves the rain and overflow colector of the gas cap.
Best regards
JAP